This invention relates to circuit breakers with ground fault interruption capability.
Ground fault circuit breakers are known in which the elements of a circuit breaker as normally devised for overload current protection are combined with the elements of a ground fault interrupter and packaged together for location at a load center. A representative example is that of Coley et al. U.S. Pat. No. 4,081,852, Mar. 28, 1978, which is incorporated by reference herein and describes an arrangement including a ground fault detector in side-by-side relation with a circuit breaker with interconnection therebetween so that breaker contacts are tripped open upon the occurrence of either a current overload condition or a ground fault condition.
Ground fault circuit breakers normally have an external handle for manual switching and for trip indication. The handle has ON, OFF, and TRIP positions so that upon a power interruption examination of the breaker will permit a user to readily determine if the breaker has tripped. Such apparatus has been widely and successfully used. It is the case, however, that a trip of the breaker is indicated in the same manner by the handle regardless of the cause of the trip, whether it be an overload condition or a ground fault condition.
A primary purpose of the present invention is to provide a ground fault circuit breaker with an indicator that shows the user if trip-out has been due to a ground fault condition, rather than an overload, so that any system condition causing a trip can be more readily identified and corrected.
Circuit breakers in accordance with the invention are provided with ground fault interruption means and overload interruption means, as heretofore, which are independently operable to open a common set of breaker contacts upon respective ground fault and overload conditions. A trip indicator that is visible external to the breaker is provided that appears only upon operation of the ground fault interruption means. The trip indicator may be a small light such as a light-emitting diode that is wired in circuit within the breaker and includes a series connection, with the light-emitting diode, including a mechanical switch arranged to close upon the opening of the breaker contacts upon either ground fault or overcurrent conditions and also including a non-mechanical, solid state, switch that becomes conductive only upon occurrence of a ground fault condition to turn on the light-emitting diode by conduction therethrough.
The solid-state switch is arranged to get a turn-on signal from the electronics which senses the occurrence of a ground fault condition. Normally this is derived from a differential current transformer as commonly used in ground fault interrupters in which the primary windings of the differential current transformer are in series with the system conductors and a sensing or secondary winding is also provided to detect current imbalance therebetween. The signals sensed on the sensing winding are normally amplified by an amplifier and then provided to a solid state switching device that energizes a trip coil for actuating the breaker trip mechanism, and, at essentially the same time, a turn-on signal is provided to the solid state switch in the indicator circuitry.
The mechanical switch in the indicating circuit branch ensures there is no power dissipation when the breaker is ON and, also, that the indicating circuit can be simply reset to OFF during the resetting of the breaker's handle. A single mechanical element that opens the breaker contacts is arranged to close the auxiliary switch.